Method for automatically locating a motor vehicle right and left wheels

ABSTRACT

A method of automatic location of the right and left wheels of a motor vehicle of the type comprising a step of automatic measurement of the centripetal acceleration of a wheel, the method being characterized in that it consists in comparing the theoretical centripetal acceleration (A i ) of a wheel in a straight line with the measured centripetal acceleration (A iv ) of this same wheel when cornering for a given vehicle speed (V), and for a given steering wheel angle (T), so as to determine whether the wheel is on the right or on the left of the vehicle.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the 35 USC 371 national stage of internationalapplication PCT/EP01/11069 filed on Sep. 25, 2001, which designated theUnited States of America.

FIELD OF THE INVENTION

The present invention relates to a method of automatic location of theright and left wheels of a motor vehicle. More especially, but notexclusively, this method is implemented in association with a system formonitoring the pressure of the tires.

BACKGROUND OF THE INVENTION

Specifically, it is already known to continuously monitor the pressureinside the tires of a vehicle. These pressure measurements (possiblycorrected as a function of the temperature and of the ageing of the tireor of any other parameter) are processed by computer and an alarm signalis emitted when the pressure of a tire is abnormal. The computerprocessing the pressure measurements can be installed on the wheelitself or at any appropriate place of the vehicle.

The pressure measurements are carried out by a specific sensorassociated with each of the wheels. The pressure measurement associatedwith a code identifying the sensor is sent to a remote computer by thissensor. Of course, it is necessary for the computer to know how toattribute this identifying code to a sensor position on the vehicle.Thus after processing, the computer must be capable of saying that thepressure measurement associated with the identifying code X originatesfrom the front right wheel (for example). To do this, it is necessaryfor the computer to learn the position, on the vehicle, of the sensorand its identifying code.

This learning can be performed manually. For example, the computer isplaced in learning mode and requests the codes of each of the pressuresensors in a preset order. This learning method is however relativelyslow. Furthermore, it must be repeated with each change of tire and hasthe drawback of compelling the driver to enter data into the computer ofthe vehicle. If the driver forgets to store the new code in memory aftera change of tire, there is a risk of error in the position of a wheelexhibiting an abnormal pressure. This may have serious consequences.

It would appear appropriate to carry out this learning of the positionof the wheels, automatically, while the vehicle is moving.

To do this, the following physical principle is used: when cornering,the inside wheels turn less quickly than the outside wheels.

However, trials carried out while allowing for the centripetalacceleration of each wheel show that deviations of speed between rightand left wheel are of the order of 1 to 10% of the measured value(acceleration).

Knowing that standard accelerometers making it possible to measure thecentripetal acceleration of the vehicle have a resolution of 1%, noiseof ±10%, an error of ±15% and exhibit drifting with temperature and withtime, it seems impossible to use the measurement of the centripetalacceleration of each wheel by using standard accelerometers, todetermine by direct comparison which wheel is turning least quickly.

It is of course possible to use more accurate accelerometers, but theaccuracy of measurement required here involves the use of very expensiveand generally very fragile accelerometers. This solution is inapplicablein the automotive environment.

The aim of the invention is therefore to determine automatically theposition of the right and left wheels of a vehicle by using standardaccelerometers.

For this purpose, the present invention relates to a method of automaticlocation of the right and left wheels of a motor vehicle of the typecomprising a step of automatic measurement of the centripetalacceleration of a wheel, said method being characterized in that itconsists in comparing the theoretical centripetal acceleration of awheel in a straight line with the measured centripetal acceleration ofthis same wheel when cornering for a given vehicle speed, and for agiven steering wheel angle, so as to determine whether said wheel is onthe right or on the left of the vehicle.

Thus, by comparing the acceleration of one and the same wheel in astraight line and when cornering, problems of dispersion of theaccuracies of the various acceleration sensors, one with respect toanother, are circumvented.

More especially, the present invention relates to a method of automaticlocation consisting firstly in:

-   -   a)—measuring the vehicle's steering wheel angle T and when this        steering wheel angle is substantially zero (vehicle in a        straight line),    -   b)—measuring the centripetal acceleration A_(i) of each of the        wheels of the vehicle with the aid of a sensor associated with        each of the wheels, and    -   c)—determining a correction coefficient k_(i) for each of the        wheels according to the following law:        A_(i)=K_(i)V²  (1)    -    where A_(i) is the straight-line centripetal acceleration        measured on wheel i, and V is the speed of the vehicle,        and consisting, subsequently, when the vehicle is cornering:    -   d)—in measuring the centripetal acceleration while cornering        A_(iv) of each of the wheels,    -   e)—in forming the difference in acceleration Δ_(i) between the        theoretical acceleration in a straight line A_(i) for a given        wheel i and a given speed V, and the acceleration measured while        cornering A_(iv) of this same wheel and at this same speed,        Δ_(i) =A _(iv) −A _(i), that is to say        Δ_(i) =A _(iv) −K _(i) V ²  (2)    -   f)—in forming the product of this difference Δ_(i) times T the        angle of the steering wheel,        (A_(iv)−K_(i)V²)×T  (3)    -   g)—in determining the sign of this product, as a function of a        chosen convention, namely; negative steering wheel angle if        cornering to the left (or the converse), and    -   h)—deducing therefrom for each of the wheels its location on the        left or right side of the vehicle.

Advantageously, a correction coefficient is calculated for each wheelwhen the vehicle is in a straight line. This makes it possible tointercompare the measurements made by the sensors on various wheelswhile circumventing, here again, errors and inaccuracies among thevarious sensors.

Advantageously, the present invention makes it possible to employstandard sensors and to obtain results with an error of less than 1%.

Advantageously, again by fixing a convention for the representation ofthe steering wheel angles (for example the negative steering wheelangles correspond to a cornering of the vehicle to the left), and bysimply determining the sign of the following product:

 (A_(iv)−K_(i)V²)×T

where A_(iv) is the measurement of the acceleration of wheel i whilecornering, K_(i)V² is the theoretical acceleration of wheel i in astraight line, and T the algebraic value of the steering wheel angle, itis possible to deduce therefrom whether the wheel i is a right or leftwheel of the vehicle.

Specifically, assuming that the convention for measuring the steeringwheel angle establishes that a cornering to the left has a negativeangle, then when the vehicle is turning to the left, we obtain T<0. Whena vehicle is turning to the left, its left wheel has a lower speed thanthis same left wheel on a straight line. Likewise, the acceleration ofthe left wheel when cornering is less than the acceleration of this sameleft wheel on a straight line. Therefore, the difference Δ_(i) betweenthe acceleration measured while cornering and the theoreticalacceleration in a straight line is less than 0. The product of T timesΔ_(i) is therefore positive.

If for this same convention for measuring the steering wheel angle theproduct T times Δ_(i) is negative it is because the wheel i is a rightwheel.

Thus, for the established convention for measuring the steering wheelangle (left=negative) the sign of the product T×Δ_(i) indicates directlythat wheel i is on the right when it is negative and that wheel i is onthe left when it is positive.

Advantageously, to improve the accuracy of the locating of the right andleft wheels, it is possible to redo the determination of the right andleft wheels a number of times and to confirm it only when the samelocation has been found several times, for a given wheel.

Advantageously again by summing a plurality of Δ_(i) of one and the samewheel and comparing this sum with all the sums of the other wheels(choosing the negative steering wheel angle preset for cornering to theleft), the largest two sums obtained correspond to the left wheels ofthe vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, characteristics and advantages of the present inventionwill emerge from the description which follows by way of nonlimitingexample and with reference to the appended drawings in which:

FIG. 1 is a diagrammatic view representing a schematic diagram of themethod according to the invention, and

FIG. 2 is a diagrammatic view representing a vehicle furnished with fouracceleration sensors.

DETAILED DESCRIPTION OF THE INVENTION

As represented in FIG. 2, a vehicle 14 is furnished with at least fourwheels 10 to 13. Each of these wheels is furnished with a standardcentripetal acceleration sensor 15 to 18. These sensors are of courseknown and will not be detailed here.

The invention starts from the following principle, the inner wheel in acorner has a lower speed than the outside wheel in the corner. Theinvention resides more precisely in the fact that: the inside wheel inthe corner has a lower speed than this same wheel when the vehicle ismoving in a straight line. It follows from this observation that theacceleration of an inside wheel in a corner is less than theacceleration of this same wheel when the vehicle is moving in a straightline.

The vehicle 14 is moreover furnished with a sensor of steering wheelangle T well known per se. This sensor is in particular necessary forthe control of power-assisted steering. It will be noted that within theframework of the present invention, it is imperative to know thedirection of rotation of the vehicle. Consequently a convention isestablished for representing the direction of rotation of the vehicle.Namely, for example, when the vehicle is turning to the left thesteering wheel angle T is negative (case represented in FIG. 2). Ofcourse the reverse convention could also have been taken.

The vehicle 14 is also furnished with a conventional tachometer.Therefore the speed of movement V of the vehicle is known.

The method according to the invention consists firstly, when the vehicleis moving in a straight line:

-   -   —in measuring the centripetal acceleration A_(i) of each of the        wheels of the vehicle with the aid of the sensor associated with        each of the wheels, and    -   c)—in determining a correction coefficient k_(i) for each of the        wheels according to the following law:        A_(i)=K_(i)V²  (1)    -    where A_(i) is the straight-line centripetal acceleration        measured on wheel i, and V is the speed of the vehicle.

According to the invention, the vehicle 14 is considered to be moving ina straight line when the steering wheel angle T is less than 5°, that isto say substantially zero.

The centripetal acceleration of each wheel is measured continuously bythe sensor associated with this wheel. Thus the centripetal accelerationA₁ of the wheel 10 is measured by the sensor 15 (likewise for each ofthe other wheels).

For each of the wheels, the correction coefficient K_(i) is calculatedas a function of the formula (1) given above. Specifically the speed Vof the vehicle being known and the acceleration A_(i) in a straight linebeing measured this coefficient K_(i) is equal to A_(i)/V².

The correction coefficient K₁ for the wheel 10, K₂ for the wheel 11, K₃for the wheel 12 and K₄ for the wheel 13 is thus determined. Of course,in order to consolidate the calculation of these coefficients, it ispossible to average them, in order in fact to find an average K_(i) foreach of the wheels.

It should be noted that the calculation of the coefficients K_(i) ofeach wheel is performed when the vehicle is moving in a straight line (Tless than 5°) since this is the only moment at which relation (1) holdscompletely.

The calculation of the coefficient K_(i) makes it possible to circumventthe disparities between various sensors, so as to obtain accelerationmeasurements which can be compared even if they originate from separatewheels.

Secondly, according to the invention, in order to further increase theaccuracy of the measurement, the theoretical acceleration of a wheel ina straight line is compared with the acceleration of this same wheelwhen cornering, rather than intercomparing the acceleration of twowheels (one being inside the corner and the other outside). This allowsany deviation in acceleration to be detected with better accuracy sincethe repeatability of a measurement with one and the same sensor isgreater than 99%.

Thus, when it is detected that the vehicle is cornering (T greater than5°), the acceleration of each wheel is measured while cornering A_(iv).

The speed V of the vehicle is measured simultaneously. The theoreticalacceleration A_(i) which this same wheel would have had if it had beenin a straight line is determined by calculation. For this purpose it issufficient to form the product K_(i)V², doing so for each wheel.

The deviation existing between the acceleration measured while corneringA_(iv) and the theoretical acceleration in a straight line A_(i) iscalculated for one and the same wheel, that is to say:A _(iv) −A _(i) =A _(iv)−(K _(i) V ²)=Δ_(i)  (2).

If the convention for representing the angles is as follows:

-   -   a steering wheel angle is negative when the vehicle is turning        to the left, then when the vehicle is turning to the left the        front left wheel 10 has a lower acceleration when cornering        A_(iv) than its acceleration A₁ in a straight line. Therefore        (A_(1iv)−A₁) is negative, that is to say Δ₁ is negative. As the        vehicle is turning to the left T is also negative! It follows        that the product T×Δ₁ is positive.

It follows from this that the sign of the product:Δ_(i)×T  (3)gives an indication of the position of wheel i.

Thus, with the convention T negative when cornering to the left, theproduct:

-   -   a) Δ_(i)×T is positive when wheel i is situated on the left of        the vehicle, and    -   b) Δ_(i)×T is negative when wheel i is situated on the right of        the vehicle.

The sign of the product Δ_(i)×T for a given wheel i, is thereforedirectly indicative of the position of this wheel.

Of course, if the reverse convention had been adopted for therepresentation of the steering wheel angles (positive steering wheelangle when the vehicle is turning to the left), it would be sufficientto reverse cases a) and b) above.

The value of the product Δ_(i)×T gives, for its part, an indication ofthe reliability index of the location found for this wheel.Specifically, the bigger the steering wheel angle T, the bigger thedeviation between the acceleration while cornering and the accelerationin a straight line. Hence, the larger the value Δ_(i)×T, the morereliable the location of the wheel arising from this measurement.

Thus, if standard sensors were employed under optimum conditions, thesign of Δ_(i)×T would be sufficient to indicate which side of thevehicle the corresponding wheel i is situated. However, this is notalways the case.

Specifically, the sign of this product often fluctuates for severalsuccessive measurements. It is not therefore always possible to locate awheel with a single measurement performed.

The present invention proposes in this case to perform the measurementsand the corresponding calculations a number of times before definitivelyruling as to the location of a wheel.

If several values of Δ_(i) are summed for wheel i, and this is done foreach of the wheels, the two largest values found correspond to the leftwheels of the vehicle (with the negative angle convention if vehicle isturning to the left). If the reverse convention had been taken, the twolargest sums would correspond to the right wheels of the vehicle.

Instead of summing the Δ_(i) for each wheel it is also possible toaverage them. If the number of measurements is sufficient (typicallygreater than 10) then the two highest values correspond to the leftwheels of the vehicle (still with the same basic convention).

When averages or a summation are done in this way, it is advantageous todelete the apparently outlying values of acceleration while corneringfrom these averages or sums. A value is considered to be an outlier ifit differs, for example, by more than 10 g (g is the acceleration due togravity) from the other values of accelerations found for the otherwheels at the same moment.

It will be noted that in order to spare the battery of the accelerationsensors, the acceleration is measured every minute for example. As soonas the right and left location of the wheels is acquired, this method oflocation is interrupted, throughout the remainder of the journey.Experience shows that after a few minutes of movement of the vehicle thelocation of the wheels is acquired.

Thereafter if one of these wheels deflates abruptly or if an abnormaltemperature and/or pressure situation arises, the computer (notrepresented) dealing with this function in the vehicle is capable ofinforming the driver that one of the right or left wheels exhibits adefect.

Of course when this method of location of the right and left wheels iscombined with a method of location of the front and rear wheels, thesystem is then automatically informed of the exact position of each ofits wheels. As soon as one of them exhibits a defect the system is thencapable of informing the driver as to the exact position of thedefective wheel.

Of course, the present invention is not limited to the embodimentsdescribed hereinabove. Thus it is possible to compare the measurementsof accelerations originating from wheels mounted on one and the sameaxle so as to detect phenomena of wheel slide or slip. Likewise thelimit value of 5°, for detecting the straight line movement of thevehicle may be slightly modified (as a function of vehicles).

1. A method of automatically determining a location of wheels of a motorvehicle (14) comprising: a step of automatic measurement of acentripetal acceleration (A_(i)) of a wheel (i) by comparing thetheoretical centripetal acceleration of the wheel in a straight line(A_(i)) with the measured centripetal acceleration of this same wheelwhen cornering (A_(iv)) for a given vehicle speed (V), and for a givensteering wheel angle (T), so as to determine whether said wheel (i) ison the right side or on the left side of the vehicle.
 2. The method ofautomatic location as claimed in claim 1, wherein said measurement stepcomprises: a)—measuring the vehicle's steering wheel angle (T), whenthis steering wheel angle is substantially zero, the vehicle being in astraight line, b)—measuring the centripetal acceleration (A_(i)) of eachof the wheels (10 to 13) of the vehicle with the aid of a sensor (15 to16) associated with each of the wheels, and c)—determining a correctioncoefficient (k_(i)) for each of the wheels according to the followinglaw:A_(i)=K_(i)V²  (1) where A_(i) is the straight-line centripetalacceleration measured on wheel i, and V is the speed of the vehicle,and, subsequently, when the vehicle is cornering d)—measuring thecentripetal acceleration while cornering (A_(iv)) of each of the wheels,e)—forming the difference in acceleration Δ_(i) between the theoreticalacceleration in a straight line (A_(i)) for a given wheel i and a givenspeed V, and the acceleration measured while cornering (A_(iv)) of thissame wheel and at this same speed,Δ_(i) =A _(iv) −K _(i) V ²  (2) f)—forming the product of thisdifference Δ_(i) times T the angle of the steering wheel,(A_(iv)−K_(i)V²)×T  (3) g)—determining the sign of this product, as afunction of a convention regarding cornering to the left or to theright, and h)—determining from the results of steps a) through g), foreach of the wheels, each wheel's location on the left or right side ofthe vehicle.
 3. The method of location as claimed in claim 2, whereinfor a given wheel, one forms the difference between the accelerationmeasured while cornering and the theoretical acceleration in a straightline multiplied by an algebraic value of the steering wheel angle todetermine whether said wheel is a right wheel or a left wheel of thevehicle.
 4. The method as claimed in claim 2, wherein, the convention isthat the sign of the steering wheel angle (T) when cornering to the leftis a negative algebraic value, and a value of the sign found in step g)being positive indicates the wheel (i) on which the acceleration hasbeen measured is a left wheel.
 5. The method as claimed in claim 2,wherein, the convention is that the sign of the steering wheel angle (T)when cornering to the left is a positive algebraic value, and a value ofthe sign found in step g) being negative indicates the wheel (i) onwhich the acceleration has been measured is a left wheel.
 6. The methodas claimed in claim 1, wherein a plurality of differences inacceleration Δ_(i) are summed for a given wheel, and the sum obtained iscompared with that of each of the other wheels.
 7. The method as claimedin claim 6, wherein the largest two sums correspond: to the left wheelsfor the convention being cornering to the left equals negative steeringwheel angle, and to the right wheels for the convention being corneringto the left equals positive steering wheel angle.
 8. The method asclaimed in claim 1, wherein for each wheel the differences inaccelerations Δ_(i) of each wheel are averaged.
 9. The method as claimedin claim 8, wherein the two largest averages correspond: to the leftwheels for the convention being cornering to the left equals negativesteering wheel angle, and to the right wheels for the convention beingcornering to the left equals positive steering wheel angle.
 10. Themethod as claimed in claim 2, wherein a plurality of differences inacceleration Δ_(i) are summed for a given wheel, and in that the sumobtained is compared with that of each of the other wheels.
 11. Themethod as claimed in claim 3, wherein a plurality of differences inacceleration Δ_(i) are summed for a given wheel, and in that the sumobtained is compared with that of each of the other wheels.
 12. Themethod as claimed in claim 4, wherein a plurality of differences inacceleration Δ_(i) are summed for a given wheel, and in that the sumobtained is compared with that of each of the other wheels.
 13. Themethod as claimed in claim 5, wherein a plurality of differences inacceleration Δ_(i) are summed for a given wheel, and in that the sumobtained is compared with that of each of the other wheels.
 14. Themethod as claimed in claim 2, wherein for each wheel the differences inaccelerations Δ_(i) of each wheel are averaged.
 15. The method asclaimed in claim 3, wherein for each wheel the differences inaccelerations Δ_(i) of each wheel are averaged.
 16. The method asclaimed in claim 4, wherein for each wheel the differences inaccelerations Δ_(i) of each wheel are averaged.
 17. The method asclaimed in claim 5, wherein for each wheel the differences inaccelerations Δ_(i) of each wheel are averaged.
 18. The method asclaimed in claim 14, wherein the two largest averages correspond: to theleft wheels for the convention being cornering to the left equalsnegative steering wheel angle, and to the right wheels for theconvention being cornering to the left equals positive steering wheelangle.
 19. The method as claimed in claim 15, wherein the two largestaverages correspond: to the left wheels for the convention beingcornering to the left equals negative steering wheel angle, and to theright wheels for the convention being cornering to the left equalspositive steering wheel angle.
 20. The method as claimed in claim 16,wherein the two largest averages correspond: to the left wheels for theconvention being cornering to the left equals negative steering wheelangle, and to the right wheels for the convention being cornering to theleft equals positive steering wheel angle.